This type of motion guide device includes a track rail having rolling surfaces for rolling elements, which are formed along a longitudinal direction of the track rail, a moving block being mounted on the track rail through intermediation of a large number of rolling elements and having formed therein endless circulation paths for the rolling elements, the large number of rolling elements arrayed inside each of the endless circulation paths, and a belt-like coupling member built into the endless circulation path together with the rolling elements, for aligning the rolling elements in line at regular intervals. Further, the coupling member includes a plurality of spacers each arranged between the adjacent rolling elements, and belt members for coupling the spacers in line at regular intervals. When the moving block reciprocates relative to the track rail, the rolling elements are caused to circulate through the endless circulation path, and the coupling member is also caused to circulate through the endless circulation path together with the rolling elements.
The endless circulation path includes a load rolling element path through which the rolling elements are caused to roll while being subjected to a load between the track rail and the moving block, a rolling element return path formed in parallel to the load rolling element path, and a pair of direction-changing paths each connecting the load rolling element path and the rolling element return path. Each direction-changing path is formed into an arc shape having a constant curvature radius so that an advancing direction of the rolling elements and the coupling member is reversed. Further, guide grooves corresponding to the belt portions of the coupling member are formed in inner walls of the load rolling element path, the rolling element return path, and the direction-changing paths along a circulating direction of the rolling elements. The coupling member is caused to circulate through the endless circulation path under a state in which the belt portions are inserted into the guide grooves. Each guide groove of the direction-changing path has its curvature center matched with the curvature center of the direction-changing path, and is formed into an arc shape having a constant curvature radius similarly to the direction-changing path.
When the coupling member is moved through the direction-changing path, the belt member is not curved into the arc shape conforming to the guide groove, but is curved into a shape analogous to the arc of the guide groove while being locally bent between the spacers adjacent to each other. Therefore, when the coupling member is moved through the direction-changing path, the belt member is liable to interfere with an outer circumferential surface of the guide groove, thereby causing a risk in that an excess sliding resistance is applied to the coupling member located inside the direction-changing path. The invention disclosed in Patent Literature 1 is provided in consideration of such interference between the belt member and the guide groove. In this invention, the curvature center of the outer circumferential surface of the guide groove is set closer to an outer circumferential surface of the direction-changing path than the curvature center of the direction-changing path, with the result that the width of the guide groove is gradually increased as approaching from both end portions of the direction-changing path to a center portion thereof, and is set to a maximum groove width at the center portion.